stl_threads.h

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    }
# else
    static inline unsigned long _Atomic_swap(unsigned long * __p, unsigned long __q) {
        unsigned long __result = *__p;
        *__p = __q;
        return __result;
    }
# endif
// GCC extension begin
#endif
// GCC extension end

// Locking class.  Note that this class *does not have a constructor*.
// It must be initialized either statically, with __STL_MUTEX_INITIALIZER,
// or dynamically, by explicitly calling the _M_initialize member function.
// (This is similar to the ways that a pthreads mutex can be initialized.)
// There are explicit member functions for acquiring and releasing the lock.

// There is no constructor because static initialization is essential for
// some uses, and only a class aggregate (see section 8.5.1 of the C++
// standard) can be initialized that way.  That means we must have no
// constructors, no base classes, no virtual functions, and no private or
// protected members.

// Helper struct.  This is a workaround for various compilers that don't
// handle static variables in inline functions properly.
template <int __inst>
struct _STL_mutex_spin {
  enum { __low_max = 30, __high_max = 1000 };
  // Low if we suspect uniprocessor, high for multiprocessor.

  static unsigned __max;
  static unsigned __last;
};

template <int __inst>
unsigned _STL_mutex_spin<__inst>::__max = _STL_mutex_spin<__inst>::__low_max;

template <int __inst>
unsigned _STL_mutex_spin<__inst>::__last = 0;

// GCC extension begin
#if defined(__STL_GTHREADS)
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
extern __gthread_mutex_t _GLIBCPP_mutex;
extern __gthread_mutex_t *_GLIBCPP_mutex_address;
extern __gthread_once_t _GLIBCPP_once;
extern void _GLIBCPP_mutex_init (void);
extern void _GLIBCPP_mutex_address_init (void);
#endif
#endif
// GCC extension end

struct _STL_mutex_lock
{
// GCC extension begin
#if defined(__STL_GTHREADS)
  // The class must be statically initialized with __STL_MUTEX_INITIALIZER.
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
  volatile int _M_init_flag;
  __gthread_once_t _M_once;
#endif
  __gthread_mutex_t _M_lock;
  void _M_initialize() {
#ifdef __GTHREAD_MUTEX_INIT
    // There should be no code in this path given the usage rules above.
#elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
    if (_M_init_flag) return;
    if (__gthread_once (&_GLIBCPP_once, _GLIBCPP_mutex_init) != 0
        && __gthread_active_p ())
      abort ();
    __gthread_mutex_lock (&_GLIBCPP_mutex);
    if (!_M_init_flag) {
	// Even though we have a global lock, we use __gthread_once to be
	// absolutely certain the _M_lock mutex is only initialized once on
	// multiprocessor systems.
	_GLIBCPP_mutex_address = &_M_lock;
	if (__gthread_once (&_M_once, _GLIBCPP_mutex_address_init) != 0
	    && __gthread_active_p ())
	  abort ();
	_M_init_flag = 1;
    }
    __gthread_mutex_unlock (&_GLIBCPP_mutex);
#endif
  }
  void _M_acquire_lock() {
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
    if (!_M_init_flag) _M_initialize();
#endif
    __gthread_mutex_lock(&_M_lock);
  }
  void _M_release_lock() {
#if !defined(__GTHREAD_MUTEX_INIT) && defined(__GTHREAD_MUTEX_INIT_FUNCTION)
    if (!_M_init_flag) _M_initialize();
#endif
    __gthread_mutex_unlock(&_M_lock);
  }
#else
// GCC extension end
#if defined(__STL_SGI_THREADS) || defined(__STL_WIN32THREADS)
  // It should be relatively easy to get this to work on any modern Unix.
  volatile unsigned long _M_lock;
  void _M_initialize() { _M_lock = 0; }
  static void _S_nsec_sleep(int __log_nsec) {
#     ifdef __STL_SGI_THREADS
          struct timespec __ts;
          /* Max sleep is 2**27nsec ~ 60msec      */
          __ts.tv_sec = 0;
          __ts.tv_nsec = 1L << __log_nsec;
          nanosleep(&__ts, 0);
#     elif defined(__STL_WIN32THREADS)
          if (__log_nsec <= 20) {
              Sleep(0);
          } else {
              Sleep(1 << (__log_nsec - 20));
          }
#     else
#       error unimplemented
#     endif
  }
  void _M_acquire_lock() {
    volatile unsigned long* __lock = &this->_M_lock;

    if (!_Atomic_swap((unsigned long*)__lock, 1)) {
      return;
    }
    unsigned __my_spin_max = _STL_mutex_spin<0>::__max;
    unsigned __my_last_spins = _STL_mutex_spin<0>::__last;
    volatile unsigned __junk = 17;      // Value doesn't matter.
    unsigned __i;
    for (__i = 0; __i < __my_spin_max; __i++) {
      if (__i < __my_last_spins/2 || *__lock) {
        __junk *= __junk; __junk *= __junk;
        __junk *= __junk; __junk *= __junk;
        continue;
      }
      if (!_Atomic_swap((unsigned long*)__lock, 1)) {
        // got it!
        // Spinning worked.  Thus we're probably not being scheduled
        // against the other process with which we were contending.
        // Thus it makes sense to spin longer the next time.
        _STL_mutex_spin<0>::__last = __i;
        _STL_mutex_spin<0>::__max = _STL_mutex_spin<0>::__high_max;
        return;
      }
    }
    // We are probably being scheduled against the other process.  Sleep.
    _STL_mutex_spin<0>::__max = _STL_mutex_spin<0>::__low_max;
    for (__i = 0 ;; ++__i) {
      int __log_nsec = __i + 6;

      if (__log_nsec > 27) __log_nsec = 27;
      if (!_Atomic_swap((unsigned long *)__lock, 1)) {
        return;
      }
      _S_nsec_sleep(__log_nsec);
    }
  }
  void _M_release_lock() {
    volatile unsigned long* __lock = &_M_lock;
#   if defined(__STL_SGI_THREADS) && defined(__GNUC__) && __mips >= 3
        asm("sync");
        *__lock = 0;
#   elif defined(__STL_SGI_THREADS) && __mips >= 3 \
         && (defined (_ABIN32) || defined(_ABI64))
        __lock_release(__lock);
#   else 
        *__lock = 0;
        // This is not sufficient on many multiprocessors, since
        // writes to protected variables and the lock may be reordered.
#   endif
  }

// We no longer use win32 critical sections.
// They appear to be slower in the contention-free case,
// and they appear difficult to initialize without introducing a race.

#elif defined(__STL_PTHREADS)
  pthread_mutex_t _M_lock;
  void _M_initialize()   { pthread_mutex_init(&_M_lock, NULL); }
  void _M_acquire_lock() { pthread_mutex_lock(&_M_lock); }
  void _M_release_lock() { pthread_mutex_unlock(&_M_lock); }
#elif defined(__STL_UITHREADS)
  mutex_t _M_lock;
  void _M_initialize()   { mutex_init(&_M_lock, USYNC_THREAD, 0); }
  void _M_acquire_lock() { mutex_lock(&_M_lock); }
  void _M_release_lock() { mutex_unlock(&_M_lock); }
#else /* No threads */
  void _M_initialize()   {}
  void _M_acquire_lock() {}
  void _M_release_lock() {}
#endif
// GCC extension begin
#endif
// GCC extension end
};

// GCC extension begin
#if defined(__STL_GTHREADS)
#ifdef __GTHREAD_MUTEX_INIT
#define __STL_MUTEX_INITIALIZER = { __GTHREAD_MUTEX_INIT }
#elif defined(__GTHREAD_MUTEX_INIT_FUNCTION)
#ifdef __GTHREAD_MUTEX_INIT_DEFAULT
#define __STL_MUTEX_INITIALIZER \
  = { 0, __GTHREAD_ONCE_INIT, __GTHREAD_MUTEX_INIT_DEFAULT }
#else
#define __STL_MUTEX_INITIALIZER = { 0, __GTHREAD_ONCE_INIT }
#endif
#endif
#else
// GCC extension end
#ifdef __STL_PTHREADS
// Pthreads locks must be statically initialized to something other than
// the default value of zero.
#   define __STL_MUTEX_INITIALIZER = { PTHREAD_MUTEX_INITIALIZER }
#elif defined(__STL_UITHREADS)
// UIthreads locks must be statically initialized to something other than
// the default value of zero.
#   define __STL_MUTEX_INITIALIZER = { DEFAULTMUTEX }
#elif defined(__STL_SGI_THREADS) || defined(__STL_WIN32THREADS)
#   define __STL_MUTEX_INITIALIZER = { 0 }
#else
#   define __STL_MUTEX_INITIALIZER
#endif
// GCC extension begin
#endif
// GCC extension end


// A locking class that uses _STL_mutex_lock.  The constructor takes a
// reference to an _STL_mutex_lock, and acquires a lock.  The
// destructor releases the lock.  It's not clear that this is exactly
// the right functionality.  It will probably change in the future.

struct _STL_auto_lock
{
  _STL_mutex_lock& _M_lock;
  
  _STL_auto_lock(_STL_mutex_lock& __lock) : _M_lock(__lock)
    { _M_lock._M_acquire_lock(); }
  ~_STL_auto_lock() { _M_lock._M_release_lock(); }

private:
  void operator=(const _STL_auto_lock&);
  _STL_auto_lock(const _STL_auto_lock&);
};

} // namespace std

#endif /* __SGI_STL_INTERNAL_THREADS_H */

// Local Variables:
// mode:C++
// End: